As is well known, in color development following the image-wise exposure of a silver halide color photographic material, the oxidized product of an aromatic primary amine color developing agent enters into coupling reaction with a color former to form a color image composed of, for example, indophenol, indoaniline, indamine, azomethine, phenoxazine, phenazine or other dyes similar thereto. In this photographic process, color reproduction is usually achieved by the substractive process using a silver halide color photographic material wherein blue-, green- and red-sensitive silver halide emulsion layers contain color formers, or couplers that will develop colors which are the respective complements of blue, green and red, namely, yellow, magenta and cyan colors.
An illustrative coupler used to form a yellow color image is acylacetanilide compound. Exemplary magenta image forming couplers include pyrazolone, pyrazolobenzimidazole, pyrazolotriazole and indazolone compounds. Among the couplers commonly used for cyan image formation are included phenolic and naphtholic compounds.
The dye images formed by the coupling reaction with such color formers and the oxidation product of aromatic primary amine color developing agent are required to undergo no discoloration or fading even if they are exposed to light or stored under hot and humid atmosphere for a prolonged period. It is also required that the background of a silver halide color photographic material (to be hereunder referred to simply as a color photographic material) or the areas where no color has formed should not undergo any yellow staining (hereunder Y staining) as a result of exposure to light or moist heat.
Magenta couplers are much more sensitive than yellow and cyan couplers to Y staining in the background caused by heat or moist heat as well as to the fading of the image areas resulting from prolonged exposure to light, and this has often caused serious problems in conventional color photography.
Couplers extensively used for magenta dye formation are 1,2-pyrazolo-5-ones. Dyes produced from such compounds generally have primary absorption at about 550 nm but they also have secondary absorption at about 430 nm. In order to minimize such secondary absorption, various efforts have been made. For example, magenta couplers having an anilino group at 3-position of 1,2-pyrazolo-5-ones have relatively small degree of secondary absorption and are particularly useful for obtaining color images in print format. Details of this technique are found in U.S. Pat. No. 2,343,703 and British Pat. No. 1,059,994. However, such substituted magenta couplers are very poor in image keeping quality, especially in the fastness of color image to light. In addition, the background is highly sensitive to Y staining.
Other magenta couplers that have been proposed as means capable of reducing the secondary absorption at about 430 nm include pyrazolobenzimidazoles (British Pat. No. 1,047,612), indazolones (U.S. Pat. No. 3,770,447), 1H-pyrazolo[5,1-c]-1,2,4-triazole type couplers (U.S. Pat. No. 3,725,067 and British Pat. Nos. 1,252,418 and 1,334,515), 1H-pyrazolo[1,5-b]-1,2,4-triazole type couplers (Research Disclosure No. 24,531) 1H-pyrazolo[1,5-c]-1,2,3-triazole type couplers (Research Disclosure No. 24,626), 1H-imidazolo[1,2-b]-pyrazole type couplers (Unexamined Published Japanese Patent Application No. 162548/1984 and Research Disclosure No. 24531), 1H-pyrazolo[1,5-b]-pyrazole type couplers (Research Disclosure No. 24230) and 1H-pyrazolo[1,5-d]-tetrazole type couplers (Research Disclosure No. 24220). Dyes formed from the 1H-pyrazolo-[5,1-c]-1,2,4-triazole type couplers, 1H-pyrazolo[1,5-b]-1,2,4-triazole type couplers, 1H-pyrazolo[1,5-c]-1,2,3-triazole type couplers, 1H-imidazolo[1,2-b]-pyrazole type couplers, 1H-pyrazolo[1,5-d]-pyrazole type couplers and 1H-pyrazolo[1,5-d]tetrazole type couplers are preferred in terms of color reproduction over dyes formed from the 1,2-pyrazolo-5-ones having an anilino group at 3-position because the former has a far smaller secondary absorption at about 430 nm. Furthermore, the background of photographic materials using these couplers as magenta couplers has extremely low sensitivity to Y staining resulting from exposure to light, heat or moisture.
However, the azomethine dye formed from these couplers has a very small degree of fastness to light. In addition, such dye is highly likely to discolor upon exposure to light and has yet to be used commercially in color photographic materials, especially in color prints which are subject to considerable degradation resulting from the discoloration of dyes.
Unexamined Published Japanese Patent Application No. 125732/1984 proposes a technique for improving the light fastness of the magenta dye image from the 1H-pyrazolo[5,1-c]-1,2,4-triazole type magenta coupler by using it in combination with a phenolic compound or a phenyl ether compound. However, even this technique is not completely satisfactory in preventing the magenta dye image from fading upon exposure to light, and is practically incapable of preventing the light discoloration of such dye image.